Thermally apertured nonwoven product and process for making same

ABSTRACT

A process for producing an apertured nonwoven fabric combines one or two outer nonwoven layer(s) with a layer of polymeric material having a lower melting temperature and a property of shrinking when melted. Heat and pressure are applied through a calender roll such that the polymeric material becomes bonded to the fibers of the nonwoven layer(s) and simultaneously shrinks and takes back the fibers away from the calendering points, thereby generating apertures through the nonwoven fabric. Preferably, the fibers are polyethylene or polypropylene fibers, and the layer of polymeric material is a thin plastic film of polyethylene stretch-wrap, elastomeric, or heat shrink material. One outer nonwoven layer may be combined with the plastic film layer to form a bi-laminate product, or two outer nonwoven layers may be combined with an intermediate plastic film to form a tri-laminate product. Low denier polypropylene/polyethylene bi-component fibers or a blend of higher and lower melting fibers may also be used. Apertured products can also be obtained with non-thermoplastic outer layers and an intermediate plastic film layer.

This is a divisional of copending application Ser. No. 08/260,126 filedJun. 15, 1994.

FIELD OF THE INVENTION

This invention relates generally to apertured nonwoven fabrics and,particularly, to an apertured nonwoven topsheet product formed by athermal aperturing process.

BACKGROUND ART

Apertured nonwoven fabrics are used in environments where it is desiredto combine the properties of a fluid pervious outer layer for contactwith the skin of a user with an absorbent layer having fluid absorptioncapacity. Such apertured nonwoven fabrics find use as a topsheet indiapers, sanitary napkins, and adult incontinence products, etc.

Traditionally, apertured nonwoven fabrics are formed by hydraulicprocesses such as hydroentangling a fibrous web with an aperturedpattern or spunlacing, by mechanical processes such as perforating orpunching a nonwoven fabric, or by thermo-mechanical processes such ashot pin perforation, embossed roll calender, etc. Hydraulic processesrequire rather costly equipment and complex processing operations.Mechanical or thermo-mechanical processes also require multipleprocessing steps, e.g., by first forming a bonded nonwoven fabric thenperforating or aperturing the same.

Some thermo-mechanical processes, such as taught in U.S. Pat. Nos.3,507,943 and 3,542,634, can bond and aperture a fibrous layer in onestep by pressure fusing the fibers of the nonwoven layer between contactpoints of embossed rolls or land-groove rolls and at the same timeforming apertures therethrough by melting with sufficient heat andpressure, shearing action, etc. However, a high amount of heat andpressure is required to produce well-formed through-holes in thenonwoven layer. Other processes, such as taught in U.S. Pat. No.4,184,902 to Karami or U.S. Pat. No. 4,780,352 to Palumbo, form atopsheet in one processing step by perforating and/or spot bonding afluid-pervious nonwoven layer with a plastic intermediate layer.However, the holes or aperture areas generated may not be of sufficientdimension or well-formed shape, and may require additional processingsuch as hot blowing or stretching to generate apertures of sufficientsize and shape.

It is therefore a principal object of the present invention to producean apertured nonwoven fabric through a one-step cost-effective processusing a simplified technique for generating apertures of sufficient sizeand shape. It is a particular object that such process take advantage ofa physical interaction between polymeric materials of different meltingtemperatures under application of heat and pressure from the calenderingpoints of an calender roll to accomplish simultaneously bonding of thefibers and forming of apertures through the nonwoven fabric.

SUMMARY OF THE INVENTION

In accordance with the present invention, a process for producing anapertured nonwoven fabric comprises the steps of combining a nonwovenlayer of fibers having a higher melting temperature and a polymericmaterial having a lower melting temperature and a property of shrinkingunder application of heat, and applying heat and pressure to thecombination of the first-mentioned fibers and the other polymericmaterial through calendering points of a calender roll, such that themelted polymeric material becomes bonded to the first-mentioned fibersand simultaneously shrinks and takes back the first-mentioned fibersaway from the calendering points, thereby generating apertures throughthe nonwoven fabric.

In the preferred process, the fibers of the nonwoven layer are cardedolefinic fibers, preferably polyethylene or polypropylene fibers, andthe layer of polymeric material is a thin plastic film of olefinicmaterial, such as a polyethylene stretch-wrap, or elastomeric material,or heat shrink material. The apertured product can have anywhere from1-50% open (apertured) area. The process can be utilized for aperturednonwoven fabrics having basis weights ranging anywhere from 10.0 to 90.0grams/yd² (gsy). One outer nonwoven layer may be combined with theplastic film layer to form a bi-laminate product, or two outer nonwovenlayers may be combined with an intermediate plastic film to form atri-laminate product.

In one particular example, the fibers of the nonwoven layer(s) arepolypropylene having a melting point of about 165° C., and the plasticfilm is a 16-gsy polyethylene stretch-wrap having a melting point of125° C. Alternatively, low denier polypropylene/polyethylenebi-component fibers or a selected blend of low and high melting fibersmay be used to obtain the same physical effect of shrinking and takingback the fibers to form apertures through the nonwoven fabric. A similareffect can be obtained when non-thermoplastic fibers in the outer layersare bonded to and pulled back by an intermediate plastic layer. Theresulting products exhibit good bonding, suitable strength, andwell-formed apertures.

Other objects, features and advantages of the present invention aredescribed in detail below in conjunction with the drawings, as follows:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a-1b illustrate the thermal aperturing technique in accordancewith the invention for the general example of a tri-laminate producthaving outer nonwoven layers and an intermediate polymeric layer.

FIG. 2 is a schematic view of a process line for the manufacture ofapertured nonwoven fabric.

FIGS. 3-8 are photographic examples of apertured nonwoven productsproduced in accordance with the thermal aperturing technique.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, a one-step bonding and aperturing process isused for manufacturing a thermally apertured nonwoven product usingthermal bonding (heated calendering) technology. The apertured nonwovenproduct is produced by combining one or two nonwoven layer(s) of fiberswith a layer of polymeric material having a lower melting temperatureand a property of shrinking when melted, such that under the applicationof heat and pressure the polymeric material becomes bonded to the fiberlayer(s) and shrinks and takes back the fibers to form apertures throughthe nonwoven fabric.

An example of the general process for forming thermally aperturingnonwoven fabric in accordance with the invention is illustrated in FIGS.1a-1d using a plastic film as the layer of polymeric material. One ortwo outer nonwoven layers 10a, 10b and a thin plastic film 12 are fed insuperposed relation through the nip of a pair of heated calender rolls20a, 20b. The calender rolls have a plurality of calendering points orlands 22a, 22b which come together to apply heat and pressure to thesuperposed layers fed in between. The fibers of the nonwoven layers aremade of a polymeric material. Preferably, they are olefinic fibers suchas polyethylene or, most preferably, polypropylene. The plastic film 12is made of a polymeric material that has a melting temperature lowerthan that of the olefinic fibers and a property of shrinking uponapplication of heat above its melting temperature. Films which can beused include olefinic, such as polyethylene stretch-wrap, elastomeric,or heat shrink films.

As shown in FIG. 1c, application of suitable heat and pressure causesthe plastic film 12 to melt and shrink away from the area of thecalendering points 20a, 20b. While shrinking back, the melting plasticfilm fuses to the fibers of the webs 10a, 10b and takes them back awayfrom the calendering points. As shown in FIG. 1d, the result is that theplastic film 12 and the fibers of the webs 10a, 10b become fused to eachother, forming a fused border 32 around the area of the calenderingpoints which serves simultaneously to bond the layers together and todefine an aperture 30 through the nonwoven fabric. The film acts as acarrier to create the aperture. On a per weight basis, some plasticfilms are cheaper than the fiber. Therefore, in some cases, the cost ofmaking the apertured fabric is significantly less than making aconventional apertured fabric of comparable weight using fibers alone.

In FIG. 2, a process line is shown schematically for the manufacture ofapertured nonwoven fabric as a continuous roll product. The olefinicfibers are carded at card stations #1 and #2 and fed on card conveyors14a, 14b, respectively, for the webs 10a, 10bof fibers. The thin plasticfilm 12 is unwound from an unwind stand 16 and fed in superposedrelation between the two carded webs on the card conveyors, and thecomposite of plastic film enclosed between two carded webs is fed byconveyors 16a, 16b to hot calender rolls 20a, 20b to be thermally bondedand apertured. The preferred practice employs dual engraved rolls(Novonette #2 pattern), although anvil rolls or even a single engravedroll may also be utilized. On entering the heated calender rolls, theolefinic fibers is bonded together and the plastic film melts andshrinks away from the calendering points to generate a pattern ofapertures. On exiting the calender rolls, the bonded and aperturednonwoven fabric is wound up on a roll.

The apertured product can be formed with typically 1-50% open(apertured) area. However, the product can be tailored with any requiredopen area by modifying the calender bond pattern, process conditions,etc. While the apertures appear to the naked eye as ovals, they are infact somewhat irregular in shape when observed under a microscope. Theapertured product can also be mechanically tentered (stretched) as itexits in a hot condition from the calender. Tentering can significantlyenhance the aperture clarity and size.

Depending on the kind of plastic film used and the type of fiberemployed, the fluid handling properties of the apertured nonwovenproduct can be modified as required for suitable strike-through, re-wet,liquid distribution, and other properties. Comparison trials showed thatapertured products can be formed having the strike-through and re-wetproperties of a typical diaper topsheet.

The fabric can be formed to possess the desired softness for skincontact in various consumer disposable applications, as measured byhand-feel. However, a trade-off exists between fabric softness and theaperture clarity that is obtained. The elasticity of the aperturedstructure can be easily altered by using elastomeric materials insteadof an olefinic film. Apertured products can be made in almost anyweight, e.g., ranging from 10.0 to 90.0 gsy. A typical fabric forconsumer disposable applications could be in the range of 35.0 to 55.0gsy.

Different variations utilizing other types of plastic films andpolymeric materials can produce apertured product using the same basicconcept of the invention. Fibers other than olefinic fibers, for examplepolyesters, polyamides, etc., may be used for the nonwoven layer. Wherea plastic film is used, apertured fabric can be made one-sided ortwo-sided. When the plastic film is embedded between two layers offiber, a soft product having the same feel on both sides is made,referred to herein as a "tri-laminate" product. On the other hand,attaching the plastic film to either side of the fiber layer results ina product having a different feel on its two sides. One side feels softdue to the presence of fibers, while the other side feels like plastic.This is referred to as a "bi-laminate" product.

It is found that using polyethylene (PE) stretch-wrap as the thin filmand embedding it between two layers of fiber gives a tri-laminateproduct with good aperture quality at the lowest cost. A desirableproduct can be made at anywhere from 30 to 46 gsy weights usinglow-elongation, high tenacity polypropylene (PP) fibers for the nonwovenlayers, such as fibers designated T101 1.8 dpf×38 mm obtained fromHercules Corp., of Norcross, Ga., and 16 gsy clear stretch wrap film,such as Loadmaster-S, PC-3400, 1.0 mil, LDPE stretch wrap film, fromBorden Packaging and Industrial Products, of North Andover, Mass.

The above-mentioned polypropylene fibers have a melting point of about165° C. (330° F.), and the polyethylene stretch-wrap has a melting pointof about 125° C. (260° F.). Optimum softness and hole clarity wereobtained at calender roll temperatures of 320° F. in particular and 300°F. to 360° F. in general when using PP fibers, and at calender rollpressures in the range of 55 psi (pounds/sq. in.) or 300 pli(pounds/linear inch).

An apertured plastic film can be used in place of the stretch wrap film.For example, apertured polytheylene (PE) films of different grades,thicknesses, and compositions with or without ethylvinyl acetate (EVA)can be used. The apertured film embedded between two layers of fibersresults in a tri-laminate product with very good aperture quality,particularly for apertured PE film with EVA. The product inherits theexcellent fluid handling characteristics of the apertured film, e.g.,good uni-directional passage of fluid. A bi-laminate variation can alsobe made.

Low denier polypropylene/polyethylene bi-component (PP/PE) fibers arealso suitable for this thermal aperturing technique. The low meltingpolyethylene sheath in contrast to the higher melting polypropylene coreacts similar to the thin olefinic film described above. In typicalexamples, cleanly apertured products were manufactured using Chisso ES0.9 dpf×38 mm bi-component fibers obtained from the Chisso Company ofJapan carded in two layers without any intermediate layer. Calender rolltemperatures of 290° F. to 295° F. were found to work best with thePP/PE bi-component fibers.

A similar variation exploits the same physical effect by blending fiberswith higher and lower melting points. The melting point differential isselected to simulate the effect of the thin olefinic film in taking backthe fibers from the aperture areas. As an example, 20% of low meltingpolyethylene fiber can be blended with 80% polypropylene fibers toproduce a suitable apertured product.

Elastic properties can be imparted to the apertured product by the useof an elastomeric film in place of the thin olefinic film. As anexample, an elastomeric film such as one designated xExx56™ obtainablefrom Exxon Chemicals Corp., of Lake Zurich, Ill., can produce a productof good aperture clarity and excellent elastic properties in both themachine and cross directions. Both tri- and bi-laminate products can bemade.

Heat shrink films may also be used to obtain the same physical effect ofshrinking and taking back the fibers to form apertures through thenonwoven fabric. For example, low-melting high-shrink films obtainedfrom Exxon Chemicals Corp. produced a product with good aperturequality. Another high shrink film, designated CLYSAR™, Grade #60LLP,from DuPont Corp., gave a unique, bulky, apertured fabric. Onlytri-laminates are possible in this case because of the shrink film'sreaction to a surface applying heat.

The above observations were made using a pilot thermal bonding line with10" width. Scaling up to a 32" wide line tested successfully. Pilot linespeeds of up to 150 feet/minute were run without any problems. The useof stretch wrap film and apertured PE film with EVA embedded in PP fiberlayers produced very good aperture quality, particularly at 32 gsyfabric weight. Calender roll temperatures of between 328° to 332° F. andcalender pressures of 400-550 pli on the 10" line and 250-300 pli on thewider thermal bonding line were found to provide optimum results. Goodaperture quality was obtained with calender lolls having the Novonettepattern and land widths of 0.065" and 0.081", for percentage ofapertured areas of 9% and 16%, respectively.

The thermal aperturing technique was also found to be adaptable totri-laminate products having non-thermoplastic fibers, e.g., rayon forthe nonwoven layers, and a suitable plastic film in between. Goodapertured products were obtained using 15 gsy Hercules T101 PP fiber inone layer and 15 gsy rayon (1.5 dpf×40 mm) fibers in the other layer,with LDPE stretch wrap, apertured PE with EVA, and elastomeric styeneblock (SB) copolymer based films. A unique product having good toexcellent aperture quality can be made with 15 gsy rayon fibers in bothlayers and an apertured PE with EVA or elastomeric SBR film in between.A product having excellent aperture quality can also be obtained withrayon fibers in both layers and a stretch wrap film in between if thecalender roll temperature is increased substantially higher, e.g., 412°F. (instead of 320° F.). A product with excellent aperture quality canalso be produced using the Hercules T101 PP fibers as the intermediatelayer, but the resulting fabric has lower tensile strengths than whenusing plastic films.

Photographic examples of the apertured products described above show theaperture quality obtained with the thermal aperturing method of thepresent invention. FIG. 3 shows a tri-laminate product obtained withpolypropylene outer layers and an intermediate thin film. FIG. 4 shows atri-laminate product with PP/PP outer layers using calender rolls of agreater land width (16% apertured area). FIG. 5 shows a bi-laminateproduct obtained with one polypropylene outer layer and an elastomericfilm. FIG. 6 shows an apertured product obtained with PP/PE bi-componentfibers in two layers without any intermediate layer. FIG. 7 shows atri-laminate product with PP and rayon outer layers and an apertured PEfilm in between. FIG. 8 shows a tri-laminate product obtained with bothouter layers of rayon fibers and an apertured PE film in between. Ineach case, good aperture quality and shape are obtained by having thethe lower melting, shrinking plastic material (thin film layer orbicomponent fiber) fusing to and pulling back the fibers of the outerlayers. The fusing and taking back of the fibers by themelting/shrinking polymeric material is evident from the crusted ring offused or congealed material surrounding the apertures and bonding thelayers together.

Although the invention has been described with reference to certainpreferred processes and examples, it will be appreciated that many othervariations and modifications thereof may be devised in accordance withthe principles disclosed herein. The invention and all such variationsand modifications thereof within the scope and spirit of the inventionare defined in the following claims.

We claim:
 1. A process for producing an apertured nonwoven fabriccomprising the steps of:combining a layer of carded fibers having afirst melting temperature and a layer of polymeric material having asecond melting temperature lower than said first melting temperature anda property of shrinking under application of heat, and applying heat andpressure to the combination of said carded fibers and said polymericmaterial through calendering points of a calender roll, such that saidpolymeric material becomes bonded to said carded fibers at saidcalendering points and simultaneously shrinks and pulls back said cardedfibers away from said calendering points, thereby forming the nonwovenfabric and generating apertures having a fused border completely throughthe nonwoven fabric.
 2. A process according to claim 1, wherein saidcarded fibers are olefinic fibers.
 3. A process according to claim 2,wherein said carded fibers are polypropylene fibers.
 4. A processaccording to claim 3, wherein said polypropylene fibers have a meltingtemperature of about 330° F.
 5. A process according to claim 1, whereinsaid polymeric material is a plastic film of olefinic material.
 6. Aprocess according to claim 1, wherein said polymeric material is aplastic film of elastomeric material.
 7. A process according to claim 1,wherein said polymeric material is a plastic film of heat shrinkmaterial.
 8. A process according to any of claims 5-7, wherein saidpolymeric material is a polyethylene stretch wrap film.
 9. A processaccording to any of claims 5-7, wherein said polymeric material is madefrom a resin comprising an elastomeric styrene block copolymer film. 10.A process according to any of claims 5-7, wherein said polymericmaterial is an apertured ethylene-vinyl acetate copolymer film.
 11. Aprocess according to claim 8, wherein said polyethylene film has amelting temperature of about 125° C.
 12. A process according to claim 1,wherein the fabric is formed by combining two outer layers of saidcarded fibers and an intermediate layer of said polymeric material,wherein said polymeric material is a plastic film.
 13. A processaccording to claim 12, wherein said carded fibers comprise olefinicfibers.
 14. A process according to claim 12, wherein one of said twoouter layers comprises olefinic fibers and another of said two outerlayers comprises non-thermoplastic fibers.
 15. A process according toclaim 12, wherein said carded fibers in said two outer layers arenon-thermoplastic fibers.
 16. A process according to claim 15, whereinsaid non-thermoplastic fibers are rayon fibers.
 17. A process accordingto claim 1, wherein the fabric is formed by combining one layer of saidcarded fibers and a layer of said polymeric material, wherein saidpolymeric material is a plastic film.
 18. A process according to claim1, wherein the fabric is formed with the layer of carded fibers andlayer of polymeric material combined as a layer of bi-component fibersmade of a lower-melting sheath and a higher-melting core.
 19. A processaccording to claim 1, wherein the fabric is formed with the layer ofcarded fibers and layer of polymeric material combined as a blend of lowand high melting fibers.
 20. A process according to claim 1, wherein thecalendering roll applies heat at a temperature in the range of 280° F.to 450° F.
 21. A process according to claim 1, wherein the calenderingroll applies pressure in the range of 200 to 600 pounds/linear-inch. 22.A process according to claim 1, wherein the apertured area is in therange of 9% to 16% of the fabric area.